The present invention generally relates to oscillator circuits, and more specifically relates to an oscillator circuit having reduced layout area and lower power supply transients.
Oscillator circuits are found in many electronic circuit applications. For example, oscillator circuits can be found in DC/DC converters, capacitive sensors, audio receivers, and FM (frequency modulation) generators, to name a few. Generally, the frequency of the oscillator is set by a capacitor. However, as the capacitor is charged and discharged during operation of some oscillator circuits, the voltage on some internal nodes can be boosted beyond the power supply rails causing abnormal behavior. To prevent excursions outside the power supply rails, attenuation capacitors have been used. However, adding attenuation capacitors increases the total amount of capacitance that is charged and discharged, resulting in large spikes in power supply current. In addition, the attenuation capacitors need to be at least as large as the capacitors used to set the frequency and therefore greatly increase the amount of surface area required to implement the oscillator circuit on an integrated circuit. In some cases, a user of an integrated circuit oscillator needs to be able to set the oscillation frequency of the oscillator. One way to make the oscillation frequency user settable is to use an external oscillation capacitor. However, because the size of the attenuation capacitor is dependent on the size of the oscillation capacitor, the user must add two external capacitors, an oscillation capacitor and an attenuation capacitor, to set the oscillation frequency. Therefore, there is a need for an integrated circuit oscillator that eliminates the need for attenuation capacitors.